The present invention relates to refractory slide gate assemblies and especially to the slide gate portions of such assemblies.
It is conventional to use slide gates for the discharge of molten metals from various metal working vessels such as bottom pouring ladles, tundishes, and the like.
Conventionally, such assemblies include a stationary refractory plate mounted to the bottom of the container and having a passage therethrough through which the molten metal can pass. A slide plate also of refractory material is slidably engaged with the lower face of the stationary plate and also has a passage therethrough which can be brought into alignment with the passage in the upper stationary plate. In some instances there is also a bottom stationary refractory plate which abuts the intermediate sliding gate plate. This bottom plate also has a passage therethrough which is aligned with the other passages to permit discharge of the molten metal from the vessel. There are associated with such plates the usual metallic mounting devices to hold the assembly in place and, of course, means provided; usually hydraulic, to move the slide gate such that its passage comes into and out of alignment with the passages in the upper and lower stationary plates to respectively permit removal or to maintain the melt in the vessel. There are a variety of different shapes and forms of such slide gates, but they all perform the essential function of permitting ready removal of the liquid melt from the container at the desired time.
There are also associated with such assemblies elements such as nozzles and the like which are also made of refractory materials.
While generally satisfactory, the refractory portions of the slide gate assembly have to be regularly replaced due to wear. This is costly and time-consuming with the slide plates and those other portions which come in contact with the molten metal wearing most rapidly. The present refractories from which the plates and other portions are made are susceptible to thermal shock and corrosion caused by contact with the molten metal.
Ceramic bonded burned magnesite plates have also been used, but these have the least thermal shock resistance of all plates. These plates are made by mixing magnesite grains with a temporary binder, pressing the mixture in the shape of the plate desired, and burning the plate at high temperature; i.e., about 2850.degree. F. or higher. The burned plate can be impregnated with tar or pitch to inhibit penetration of the pore structure of the plate by metal and slag during use. The impregnated shapes are often baked at about 600.degree. to 850.degree. F. or higher prior to use to reduce or eliminate the volatiles and/or drainage of the tar or pitch. But these plates are also very prone to thermal shock damage which contributes to their wear. The movement of the passing metal; such as steel, and slag can cause heavy corrosion due both to the physical and chemical activity of the molten metal and, thus, causes deterioration of these plates requiring, as noted, their replacement. This is a costly and time-consuming process and efforts to prolong the life of such refractory plates have not been successful.